Re: [PATCH] oom: add sysctl to enable slab memory dump
From: Pekka Enberg <penberg@kernel.org>
Date: 2012-02-22 13:17:40
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On Wed, Feb 22, 2012 at 1:53 PM, Rafael Aquini [off-list ref] wrote:
Adds a new sysctl, 'oom_dump_slabs', that enables the kernel to produce a dump of all eligible system slab caches when performing an OOM-killing. Information includes per cache active objects, total objects, object size, cache name and cache size. The eligibility for being reported is given by an auxiliary sysctl, 'oom_dump_slabs_ratio', which express (in percentage) the memory committed ratio between a particular cache size and the total slab size. This, alongside with all other data dumped in OOM events, is very helpful information in diagnosing why there was an OOM condition specially when kernel code is under investigation. Signed-off-by: Rafael Aquini <redacted>
Makes sense. Do you have an example how an out-of-memory slab cache dump looks like?
quoted hunk ↗ jump to hunk
diff --git a/mm/slab.c b/mm/slab.c index f0bd785..c2b5d14 100644 --- a/mm/slab.c +++ b/mm/slab.c@@ -4629,3 +4629,75 @@ size_t ksize(const void *objp)return obj_size(virt_to_cache(objp)); } EXPORT_SYMBOL(ksize); + +/** + * oom_dump_slabs - dump top slab cache users + * @ratio: memory committed ratio between a cache size and the total slab size + * + * Dumps the current memory state of all eligible slab caches. + * State information includes cache's active objects, total objects, + * object size, cache name, and cache size. + */ +void oom_dump_slabs(int ratio) +{ + struct kmem_cache *cachep; + struct kmem_list3 *l3; + struct slab *slabp; + unsigned long active_objs, num_objs, free_objects, cache_size; + unsigned long active_slabs, num_slabs, slab_total_mem; + int node;
[snip]
+ list_for_each_entry(cachep, &cache_chain, next) {
+ num_objs = 0;
+ num_slabs = 0;
+ active_objs = 0;
+ free_objects = 0;
+ active_slabs = 0;Minor style nit: just define the zeroed variables in this block.
+
+ for_each_online_node(node) {
+ l3 = cachep->nodelists[node];
+ if (!l3)
+ continue;
+void oom_dump_slabs(int ratio)
+{
+ unsigned long cache_size, slab_total_mem;
+ unsigned long nr_objs, nr_free, nr_inuse;
+ struct kmem_cache *cachep;
+ int node;
+
+ slab_total_mem = (global_page_state(NR_SLAB_RECLAIMABLE) +
+ global_page_state(NR_SLAB_UNRECLAIMABLE)) << PAGE_SHIFT;
+
+ if (ratio < 0)
+ ratio = 0;
+
+ if (ratio > 100)
+ ratio = 100;
+
+ pr_info("--- oom_dump_slabs:\n");
+ pr_info("<active_objs> <num_objs> <objsize> <cache_name>\n");
+ down_read(&slub_lock);
+ list_for_each_entry(cachep, &slab_caches, list) {
+ nr_objs = 0;
+ nr_free = 0;ditto.
+
+ for_each_online_node(node) {
+ struct kmem_cache_node *n = get_node(cachep, node);
+ if (!n)
+ continue;
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